1. Field of the Invention
The present invention relates to a communication system constructed by connecting, via a data transmission line, between plural communication apparatuses to which terminal apparatuses are connected respectively and employing asynchronous mode as a media access control system and, more particularly, a transmitter, a receiver, a communication apparatus, a communication method and a communication system, capable of executing smooth data exchange between any terminal apparatuses in real time even if a data transmission line having relatively small transmission capacity is employed.
2. Description of the Prior Art
In recent years, a digital satellite broadcast which can broadcast digital data as a broadcasting object including video, sound, character, etc. via satellite radio wave has been rapidly spread. In broadcasting digital data, the enterprise for delivering the digital satellite broadcast first performs a predetermined conversion process of the digital data as broadcast object. Such conversion process will be explained in brief. The digital data as the broadcast object is first compressed (low-bit-rate coded) in terms of MPEG2 (Moving Picture Image Coding Experts Group Phase 2) which is a moving picture compression method employed in a digital TV set, a DVD (Digital Video Disc, or Digital Versatile Disc) player, etc., and then such compressed data are converted into bit stream data which are packeted by adding header information including synchronizing signals according to the standard of the MPEG2. The bit stream data are multiplexed in compliance with the standard of MPEG2 Systems which is used to multiplex video data, sound data, and other data being coded by MPEG2, then predetermined processes of multiplexed MPEG2 data such as modulation, etc. are performed, and then such processed data are transmitted from an earth station to a communication satellite as broadcast radio waves.
Meanwhile, the receiver of the digital satellite broadcast receives the satellite radio waves transmitted from the communication satellite by using a tuner module via an antenna, and then the received MPEG2 data are subject to a predetermined inverse conversion process. Such inverse conversion process will be explained in brief. At first, the header information of the received MPEG2 data are decoded so as to output the synchronizing signals and the compressed bit stream data separately. The compressed bit stream data which are output in synchronism with the output synchronizing signals are decoded by an MPEG2 decoder and then expanded into the digital data form before the compression has been effected. Next, the expanded digital data are converted in analog signals and then input into a monitor. Received video, sound, etc. are reproduced by the monitor.
At any rate, recently such a request is increasing that the digital data, e.g., digital data received via the above digital satellite broadcast, digital data reproduced by the DVD player, etc., in which the synchronizing signals and the bit stream data are separated, should be handled in terms of a centralization process employing an asynchronous mode as the media access control system in a communication system, which is constructed by connecting plural communication apparatuses including a personal computer, etc. for example, via the data transmission line. This is because it is convenient to commonly use mutual output data in plural communication apparatuses if the communication system can be so constructed that the digital data being sent out from respective communication apparatuses can be exchanged among respective communication apparatuses and in addition it is advantageous to transmit multimedia data including sound, moving picture, etc. in real time if the asynchronous mode can be employed as the media access control system.
However, in order to satisfy the request that the digital data in which the synchronizing signals and the bit stream data are separated should be handled based on centralization process employing an asynchronous mode as the media access control system in the conventional communication system, there is necessity of employing a data transmission line with relatively large transmission capacity which enables transmission of data such as moving picture having a large quantity of information. As a consequence, there have been to-be-overcome problems that a margin in design is limited to construct the communication system and also the conventional communication system is disadvantageous in a cost aspect.